ASTM D785-98e1

NOTICE: This standard has either been superceded and replaced by a new version or discontinued.
Contact ASTM International (www.astm.org) for the latest information.
e1
Designation: D 785 – 98
Standard Test Method for
Rockwell Hardness of Plastics and Electrical Insulating
Materials
This standard is issued under the fixed designation D 785; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (e) indicates an editorial change since the last revision or reapproval.
e NOTE—Editorially corrected typographical error in 12.2 in April 2002.
1. Scope 2.2 ISO Standards
ISO 2039-2 Plastics— Determination of Hardness—Part 2:
1.1 This test method covers two procedures for testing the
Rockwell Hardness
indention hardness of plastics and related plastic electrical
insulating materials by means of the Rockwell hardness tester.
3. Terminology
1.2 The values stated in SI units are to be regarded as the
3.1 Definitions used in this test method are in accordance
standard. The values given in parentheses are for information
with Terminology D 883.
only.
1.3 This standard does not purport to address all of the
4. Significance and Use
safety concerns, if any, associated with its use. It is the
4.1 A Rockwell hardness number is a number derived from
responsibility of the user of this standard to establish appro-
the net increase in depth impression as the load on an indenter
priate safety and health practices and determine the applica-
is increased from a fixed minor load to a major load and then
bility of regulatory limitations prior to use.
returned to a minor load (Procedure A). A Rockwell alpha (a)
NOTE 1—This test method and ISO 2039-2 are equivalent.
hardness number represents the maximum possible remaining
travel of a short-stroke machine from the net depth of impres-
2. Referenced Documents
sion, as the load on the indenter is increased from a fixed minor
2.1 ASTM Standards:
load to a major load (Procedure B). Indenters are round steel
D 617 Test Method for Punching Quality of Phenolic Lami-
balls of specific diameters. Rockwell hardness numbers are
nated Sheets
always quoted with a scale symbol representing the indenter
D 618 Practice for Conditioning Plastics and Electrical
size, load, and dial scale used. This test method is based on Test
Insulating Materials for Testing
Methods E 18. Procedure A (Section 11) yields the indentation
D 883 Terminology Relating to Plastics
of the specimen remaining 15 s after a given major load is
D 2240 Test Method for Rubber Property—Durometer
released to a standard 10-kg minor load. Procedure B (Section
Hardness
12) yields the indentation of the indenter into the specimen
D 4000 Classification System for Specifying Plastic Mate-
after a 15-s application of the major load while the load is still
rials
applied. Each Rockwell scale division represents 0.002-mm
E 18 Test Methods for Rockwell Hardness and Rockwell
(0.00008-in.) vertical movement of the indenter.
Superficial Hardness of Metallic Materials
4.2 A Rockwell hardness number is directly related to the
E 691 Practice for Conducting an Interlaboratory Study to
indentation hardness of a plastic material, with the higher the
Determine the Precision of a Test Method
reading the harder the material. An a hardness number is equal
to 150 minus the instrument reading. Due to a short overlap of
Rockwell hardness scales by Procedure A, two different dial
1 readings on different scales may be obtained on the same
This method is under the jurisdiction of ASTM Committee D20 on Plastics and
material, both of which may be technically correct.
is the direct responsibility of Subcommittee D20.10 on Mechanical Properties.
Current edition approved May 10, 1998. Published March 1999. Originally
4.3 For certain types of materials having creep and recovery,
e1
published as D785-44. Last previous edition D785-93 .
the time factors involved in applications of major and minor
Annual Book of ASTM Standards, Vol 10.01.
loads have a considerable effect on the results of the measure-
Annual Book of ASTM Standards, Vol 08.01.
Annual Book of ASTM Standards, Vol 09.01. ments.
Annual Book of ASTM Standards, Vol 08.02.
Annual Book of ASTM Standards, Vol 03.01.
Annual Book of ASTM Standards, Vol 14.02.
Available from American National Standard Institute, 11 W. 42nd St., 13th
Floor, New York, NY 10036.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
NOTICE: This standard has either been superceded and replaced by a new version or discontinued.
Contact ASTM International (www.astm.org) for the latest information.
D 785
4.4 The results obtained by this test method are not gener- may be reported, but the corresponding correct readings shall
ally considered a measure of the abrasion or wear resistance of
follow in parentheses, if possible. Such alternate readings are
the plastic materials in question.
not always feasible when the specimen is subjected to con-
4.5 Indentation hardness is used as an indication of cure of
stantly changing conditions or irreversible reactions.
some thermosetting materials at room temperature. Generally,
NOTE 2—Molded specimens containing coarse fiber fillers, such as
an uncured specimen has a hardness reading below normal.
woven glass fabric, will influence the penetration obtained. These varia-
4.6 Indentation hardness may be used as a control test for
tions in hardness may be reduced by testing with the largest ball indenter
indicating the punching quality of laminated sheet stock at the
consistent with the overall hardness of the material.
processing temperature. Test methods are given in Test Method
5.2 If the bench or table on which a Rockwell hardness
D 617.
tester is mounted is subject to vibration, such as is experienced
4.7 Each Rockwell hardness scale in Table 1 is an extension
of the proceeding less severe scale, and while there is some in the vicinity of other machines, the tester should be mounted
on a metal plate with sponge rubber at least 25 mm (1 in.)
overlap between adjacent scales, a correlation table is not
desirable. Readings on one material may be satisfactory for thick, or on any other type of mounting that will effectually
such a table, but there is no guarantee that other plastic eliminate vibration from the machine. Otherwise the indenter
materials will give corresponding readings because of differ-
will indent further into the material than when such vibrations
ences in elasticity, creep, and shear characteristics.
are absent.
4.8 Before proceeding with this test method, reference
5.3 Dust, dirt, grease, and scale or rust should not be
should be made to the specification of the material being tested.
allowed to accumulate on the indenter, as this will affect the
Any test specimen preparation, conditioning, dimensions,
results. Steel ball indenters that have nicks, burrs, or are out of
and/or testing parameters covered in the materials specification
round shall not be used.
shall take precedence over those mentioned in this test method.
5.4 The condition of the test equipment is an important
If there are no material specifications, then the default condi-
factor in the accuracy of the test results. Dust, dirt or heavy oil
tions apply.
act as a cushion to the load supporting members of the test
equipment and cause erroneous readings of the instrument dial.
5. Factors Affecting Reproducibility and Accuracy
The shoulders of the instrument housing, indenter chuck, ball
5.1 Rockwell hardness readings have been found reproduc-
seat in the instrument housing, capstan, capstan screw, and
ible to 62 divisions for certain homogeneous materials with a
5 anvil shoulder seat should be kept clean and true. The capstan
Young’s modulus in compression over 3400 MPa (5 3 10
and screw should be lightly oiled. Pitted anvil surfaces may be
psi). Softer plastics and coarse-filled materials will have a
refinished with 600 grit paper.
wider range of variation. A large ball indenter will distribute
5.5 Surface conditions of the specimen have a marked effect
the load more evenly and decrease the range of test results
on the readings obtained in a test. Generally, a molded finish
(Note 2). The sensitivity of the instrument decreases with an
will give a higher Rockwell reading than a machined face due
increase in the dial reading and becomes very poor for readings
to the high resin content or filled materials or better orientation
of 100 and over due to the shallow indentation of the steel ball.
and lower plasticizer content of unfilled plastic materials.
It is desirable to use the smallest ball and highest load that is
practical because of this loss of sensitivity. Rockwell hardness Tubular or unsupported curved specimens are not recom-
mended for plastic hardness testing. Such curved surfaces have
readings over 115 are not satisfactory and shall not be reported.
Readings between zero and 100 are recommended, but read- a tendency to yield with the load and produce an unsymmetri-
ings to 115 are permissible. For comparison purposes, it may cal indentation pattern.
be desirable to take readings higher than 115 or lower than zero
5.6 Many plastic materials have anisotropic characteristics
on any single scale. In such cases, Rockwell hardness readings
which cause indentation hardness to vary with the direction of
testing. In such cases, the hardest face is generally that one
perpendicular to the molding pressure. Specimens with flash-
TABLE 1 Rockwell Hardness Scales
ing on the side supported by the anvil also may give erroneous
Rockwell Indenter Diameter
Hardness Minor Major
results.
Scale Load, Load,
A 5.7 Ambient temperature variations can significantly affect
(Red Dial kg kg
in. mm
Numbers)
hardness for many materials.
R 10 60 0.5000 6 12.700 6
5.8 Rockwell hardness tests of the highest accuracy are
0.0001 0.0025
made on pieces of sufficient thickness so that the Rockwell
L 10 60 0.2500 6 6.350 6
reading is not affected by the supporting anvil. A bulge, change
0.0001 0.0025
M 10 100 0.2500 6 6.350 6
in color, or other marking on the under surface of the test
0.0001 0.0025
specimen closest to the anvil is an indication that the specimen
E 10 100 0.1250 6 3.175 6
0.0001 0.0025 is not sufficiently thick for precision testing. Stacking of thin
K 10 150 0.1250 6 3.175 6
specimen is permitted provided they are flat, parallel, and free
0.0001 0.0025
from dust or burrs. The precision of the test is reduced for
A
This major load is not the sum of the actual weights at the back of the frame but
stacked specimens, and results should not be compared to a test
is a ratio of this load, depending on the leverage arm of machine. One make and
model has a 25 to 1 leverage arm. specimen of standard thickness.
NOTICE: This standard has either been superceded and replaced by a new version or discontinued.
Contact ASTM International (www.astm.org) for the latest information.
D 785
6. Apparatus tests against the hardness calibration of the blocks. If the error
is more than 62 hardness numbers, bring the machine into
6.1 Rockwell Hardness Tester, in accordance with the re-
adjustment as described in 8.4 or in 5.3 and 5.4. If adjustment
quirements of Section 7. A flat anvil at least 50 mm (2 in.) in
can not be achieved, more extensive servicing of the instru-
diameter shall be used as a base plate for flat specimens.
ment may be needed.
6.2 For Rockwell hardness testing, it is necessary that the
major load, when fully applied, be completely supported by the
NOTE 4—Standard test blocks for the R, L, E, K, and M scales are
specimen and not held by other limiting elements of the available from Wilson Instruments, 100 Royal Street, Canton, Ma 02021
(A Division of Instron Corporation).
machine. To determine whether this condition is satisfied, the
major load should be applied to the test specimen. If an
8.4 Check the index lever adjustment periodically and make
additional load is then applied, by means of hand pressure on
adjustments if necessary. To adjust the index lever, place a
the weights, the needle should indicate an additional indenta-
specimen (plastic with low creep or soft metal) on the anvil and
tion. If this is not indicated, the major load is not being applied
turn the knurled elevating ring to bring the specimen in contact
to the specimen, and a long-stroke (PL) machine or less severe
with the indenter. Keep turning the ring to elevate the specimen
scale should be used. For the harder materials with a modulus
until positive resistance to further turning is felt, which will be
around 5500 MPa (8 3 10 psi) or over, a stroke equivalent to
after the 10-kg load is encountered. When excessive power
150 scale divisions, under major load application, may be
would have to be used to raise, the specimen higher, set the dial
adequate; but for softer materials the long-stroke (250 scale
so that the set position is at the top and take note of the position
divisions under major load) machine is required.
of the pointer on the dial. If the pointer is between B 50 and B
70 on the red scale, no adjustment is necessary; if the pointer
7. Test Specimen
is between B 45 and B 50, adjustment is advisable; and if the
7.1 The standard test specimen shall have a minimum
pointer is anywhere else, adjustment is imperative. As the
thickness of 6 mm ( ⁄4 in.). The specimen may be a piece cut
pointer revolves several times when the specimens is elevated,
from a molding or sheet. Care should be taken that the test
the readings mentioned above apply to the revolution of the
specimen has parallel flat surfaces to ensure good seating on
pointer which occurs either as the reference mark on the gage
the anvil and thus avoid the deflection that may be caused by
stem disappears into the sleeve or as the auxiliary hand on the
poor contact. The specimen shall be at least 25 mm (1 in.)
dial passes beyond the zero setting on the dial. The object of
2 2
square if cut from sheet stock, or at least 6 cm (1 in. ) in area
this adjustment is to determine if the elevation of the specimen
if cut from other shapes. The minimum width shall be 13 mm
to the minor load does not cause even a partial application of
( ⁄2 in.) plus the width of the indentation resulting from the
the major load. Apply the major load only through the release
conduct of a test using the chosen indenter.
mechanism.
NOTE 3—Specimen with a thickness other than 6 mm may be used if it
has been verified that, for that thickness, the hardness values are not
9. Conditioning
affected by the supporting surface and that no imprint shows under the
9.1 Conditioning—Condition the test specimens at 23 6
surface of the specimen after testing. The specimen may be composed of
...